Author: hiren
Date: Tue Oct 18 02:40:25 2016
New Revision: 307545
URL: https://svnweb.freebsd.org/changeset/base/307545

Log:
  Make sure tcp_mss() has the same check as tcp_mss_update() to have t_maxseg 
set
  to at least 64.
  
  This is still just a coverup to avoid kernel panic and not an actual fix.
  
  PR:                   213232
  Reviewed by:          glebius
  MFC after:            1 week
  Sponsored by:         Limelight Networks
  Differential Revision:        https://reviews.freebsd.org/D8272

Modified:
  head/sys/netinet/tcp_input.c

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c        Tue Oct 18 01:55:07 2016        
(r307544)
+++ head/sys/netinet/tcp_input.c        Tue Oct 18 02:40:25 2016        
(r307545)
@@ -3758,7 +3758,15 @@ tcp_mss(struct tcpcb *tp, int offer)
                        (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
        }
        SOCKBUF_UNLOCK(&so->so_snd);
-       tp->t_maxseg = mss;
+       /*
+        * Sanity check: make sure that maxseg will be large
+        * enough to allow some data on segments even if the
+        * all the option space is used (40bytes).  Otherwise
+        * funny things may happen in tcp_output.
+        *
+        * XXXGL: shouldn't we reserve space for IP/IPv6 options?
+        */
+       tp->t_maxseg = max(mss, 64);
 
        SOCKBUF_LOCK(&so->so_rcv);
        if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
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